The present invention relates to a parallel plate type oscillatory gyroscope, and more particularly, to a highly sensitive parallel plate type oscillatory gyroscope.
A conventional tuning-fork type oscillatory gyroscope is shown in FIG. 1. As shown in FIG. 1, the tuning-fork type oscillatory gyroscope 21 includes a pair of piezoelectric ceramic driving plates 23, the base ends of which are connected to each other by a connection plate 22. The driving plates 23 are parallel to each other and their planes are normal to the X-axis, as shown in FIG. 1. A pair of piezoelectric ceramic detection plates 24 are located on centers of the distal ends of the driving plates 23, respectively. The detection plates 24 lie in a plane normal to the Y-axis, which is perpendicular to the X-axis, as shown in FIG. 1. Alternating voltage is applied to the driving plates 23, which causes them to oscillate in the positive and negative directions of the X-axis. If rotation about the Z-axis is imparted to the oscillatory gyroscope 21, the detection plates 24 distort and produce a voltage. Detection of this voltage permits a force acting on the detection plates 24, or, a Coriolis force Fc, to be sensed. The Coriolis force Fc is generally represented by the following formula (1): EQU Fc=2mV.times..omega. (1)
where m indicates the mass of the oscillatory gyroscope 21, V indicates the oscillating rate, and .omega. indicates the angular velocity of the oscillatory gyroscope 21 about the Z-axis.
The plates 23, 24 are formed from bulk PZT (lead zirconate titanate, or ceramics containing a solid solution of lead titanate and lead zirconate). However, it is difficult to form bulk PZT into thin plates and thus difficult to reduce the size of the oscillatory gyroscope.
Furthermore, each driving plate 23 must be perpendicular to the associated detection plate 24. Each set of associated plates 23, 24 must also be symmetric. This complicates assembly. In addition, if the oscillating element has a three-dimensional structure, the bulk PZT further complicates assembly.
As apparent from formula (1), the Coriolis force Fc increases proportionally to the mass m of the oscillatory gyroscope. Thus, a greater mass m increases the distortion amount of the detection plates 24 and increases the detecting sensitivity. However, the employment of a larger bulk PZT to increase the mass of the oscillatory gyroscope is undesirable.
It is also apparent from formula (1) that the Coriolis force Fc increases proportionally to the oscillating rate V. Thus, a higher oscillating rate V increases the distortion amount of the detection plates 24 and improves the detection sensitivity. The oscillating rate V can be increased by using a thinner bulk PZT. However, this would decrease the rigidity of the driving plates 23. The driving plates 23 apt to twist if they are less rigid. Such twisting would cause vibrations that interfere with accurate voltage detection when the detection plates 24 distort.